20-MHz high-intensity focused ultrasound for seborrheic keratoses of the head and neck: outcomes and dermoscopic predictors.

Introduction: Seborrheic keratoses (SKs) are common benign epidermal tumours that frequently require removal for cosmetic reasons and are located on the head and neck. Conventional destructive methods may cause scarring or dyspigmentation. High-frequency (20 MHz) high-intensity focused ultrasound (HIFU) is a novel non-invasive modality, but evidence for SK is limited. Aim: To assess the effectiveness and safety of HIFU for head-and-neck SKs and to identify baseline dermoscopic predictors of complete clearance, including anatomical site effects. Material and methods: In this single-centre retrospective study, 178 SK lesions from 38 patients treated with 20 MHz HIFU were analysed. Outcomes were derived from clinical and photographic follow-up. Mixed-effects logistic regression was used to identify independent predictors of complete clearance, with anatomical location as a fixed effect and patient as a random intercept. Results: Complete clearance was achieved in 74.7% (133/178) of lesions and 14.0% showed near-complete response. Clearance differed by location, with lower complete clearance on the scalp (40%) compared with the face and neck (78%). Overall cosmetic outcomes were favourable (good/excellent in 86.0%). Adverse effects were common but mostly mild, with hypopigmentation being the most frequent. In mixed-effects models, a sharp border (OR ≈ 2.5, Conclusions: HIFU is a promising treatment for SKs in cosmetically sensitive areas, providing high clearance with favourable cosmetic outcomes. Anatomical location and baseline dermoscopy can support patient selection and treatment-parameter tailoring.